Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 781: Which phases occur in the sequence: rapid filling followed by atrial contraction?

A. Isovolumic contraction, Diastasis
B. Isovolumic relaxation, Ejection
C. Atrial systole, Ejection
D. Rapid filling, Atrial contraction (Correct Answer)

Explanation: ***Rapid filling, Atrial contraction*** - **Rapid filling** is the early diastolic phase when blood flows passively from the atria into the ventricles immediately after the AV valves open. - **Atrial contraction** (atrial systole) is the final phase of ventricular filling, contributing the last 20-30% of ventricular volume. - These two phases occur in this exact sequence during ventricular diastole, directly matching the question. *Atrial systole, Ejection* - While **atrial systole** is the same as atrial contraction, **ejection** does not immediately follow it. - Between atrial systole and ejection, there is an **isovolumic contraction** phase where ventricular pressure rises with all valves closed. - This sequence skips a critical intermediate phase. *Isovolumic contraction, Diastasis* - **Isovolumic contraction** occurs after atrial contraction but before ejection. - **Diastasis** is the slow filling phase that occurs between rapid filling and atrial contraction. - This sequence does not represent the phases mentioned in the question. *Isovolumic relaxation, Ejection* - **Isovolumic relaxation** occurs immediately after ejection ends, when ventricular pressure drops with all valves closed. - **Ejection** precedes isovolumic relaxation, not follows it. - This sequence is physiologically incorrect and unrelated to the question.

Question 782: What is the correct sequence of phases that follows isovolumic contraction in the cardiac cycle?

A. Ejection, Isovolumic relaxation (Correct Answer)
B. Rapid filling, Diastasis
C. Atrial systole, Isovolumic contraction
D. Diastasis, Atrial systole

Explanation: ***Ejection, Isovolumic relaxation*** - Following **isovolumic contraction**, ventricular pressure exceeds aortic pressure, causing the aortic valve to open and blood to be ejected from the ventricle. - After ejection, the aortic valve closes, and the ventricle relaxes without a change in volume, leading to **isovolumic relaxation**. *Rapid filling, Diastasis* - These phases occur during **ventricular diastole**, specifically after isovolumic relaxation, when the mitral valve opens and blood flows from the atria into the ventricles. - They represent the filling stages of the cardiac cycle, not the immediate phases after isovolumic contraction. *Diastasis, Atrial systole* - **Diastasis** is a late phase of ventricular filling, where blood flows slowly into the ventricles. - **Atrial systole** (atrial contraction) occurs at the very end of ventricular diastole, just before isovolumic contraction, to push the final volume of blood into the ventricles. *Atrial systole, Isovolumic contraction* - **Atrial systole** precedes **isovolumic contraction** in the cardiac cycle. - Isovolumic contraction is the phase where ventricular pressure rapidly increases while volume remains constant, just before blood is ejected.

Question 783: How does pulmonary hypertension contribute to hemoptysis?

A. Increased alveolar pressure
B. Increased bronchial artery pressure (Correct Answer)
C. Elevated pulmonary venous pressure
D. Vasoconstriction of pulmonary arteries

Explanation: ***Increased bronchial artery pressure*** - In chronic **pulmonary hypertension**, bronchial arteries undergo **hypertrophy and develop extensive collateral circulation** to compensate for reduced pulmonary blood flow. - These hypertrophied bronchial arteries are **high-pressure systemic vessels** (unlike the low-pressure pulmonary circulation) and can form **bronchopulmonary anastomoses**. - **Rupture of these dilated, thin-walled bronchial vessels** is the primary mechanism of hemoptysis in pulmonary hypertension, particularly massive hemoptysis. - This is commonly seen in conditions like **chronic pulmonary thromboembolism, Eisenmenger syndrome**, and other causes of chronic pulmonary hypertension. *Elevated pulmonary venous pressure* - **Elevated pulmonary venous pressure** causes hemoptysis in **left heart failure and mitral stenosis**, not in primary pulmonary arterial hypertension. - Pulmonary arterial hypertension is a **pre-capillary condition** affecting arteries; pulmonary venous pressure is typically normal or low. - This option confuses pulmonary arterial hypertension with pulmonary venous hypertension (post-capillary), which are distinct pathophysiologic entities. *Increased alveolar pressure* - Increased alveolar pressure (e.g., from **mechanical ventilation with high PEEP**) causes **barotrauma** leading to pneumothorax or pneumomediastinum. - This is **unrelated to pulmonary hypertension** and does not cause hemoptysis through the vascular mechanisms seen in pulmonary hypertension. *Vasoconstriction of pulmonary arteries* - **Vasoconstriction is a key feature** of pulmonary arterial hypertension pathophysiology, contributing to elevated pulmonary artery pressure. - However, vasoconstriction itself does not directly cause vessel rupture; rather, it is the **chronic high pressure leading to bronchial artery collateralization** that results in hemoptysis. - The thick-walled pulmonary arteries are less prone to rupture compared to thin-walled bronchial collaterals.

Question 784: What is the primary pulmonary mechanism by which left-sided heart failure causes dyspnea?

A. Reduced lung compliance due to fluid accumulation in the lungs (Correct Answer)
B. Narrowing of the airways
C. Elevated pressure in the pulmonary circulation
D. Increased pressure in the systemic circulation

Explanation: ***Reduced lung compliance due to fluid accumulation in the lungs*** - Left-sided heart failure causes **pulmonary venous congestion**, leading to fluid leaking into the interstitial spaces and alveoli of the lungs, known as **pulmonary edema**. - This fluid accumulation makes the lungs stiffer and harder to expand, thereby **reducing lung compliance** and increasing the work of breathing, resulting in dyspnea. - This is the **primary pulmonary/respiratory mechanism** that directly impairs ventilation. *Narrowing of the airways* - While **bronchoconstriction** can occur in some patients with heart failure ("cardiac asthma"), it is not the primary mechanism by which left-sided heart failure causes dyspnea. - The main issue is fluid in the lung parenchyma affecting compliance, not primarily spasm or narrowing of the airways. *Elevated pressure in the pulmonary circulation* - This is the **upstream cardiovascular mechanism** that drives fluid accumulation, not the direct pulmonary mechanism itself. - Elevated pulmonary capillary hydrostatic pressure causes fluid transudation, but the **resulting reduced lung compliance** is what directly impairs breathing mechanics. - The question asks for the pulmonary mechanism, making this answer incomplete. *Increased pressure in the systemic circulation* - **Systemic hypertension** is a risk factor for left-sided heart failure but does not directly explain the pulmonary pathophysiology causing dyspnea. - Increased systemic pressure primarily affects the **afterload** on the left ventricle, which can lead to heart failure, but it is not the mechanism of breathlessness.

Question 785: During the cardiac cycle, which phase corresponds to the period when the ventricles are contracting but no blood is being ejected?

A. Isovolumetric relaxation phase
B. Ventricular ejection phase
C. Atrial contraction phase
D. Isovolumetric contraction phase (Correct Answer)

Explanation: ***Isovolumetric contraction phase*** - During this phase, the **ventricular muscles contract**, leading to a rapid increase in intraventricular pressure. - Both the **mitral/tricuspid (AV) valves** and the **aortic/pulmonic (semilunar) valves** are closed, preventing blood ejection. *Isovolumetric relaxation phase* - This phase occurs during **diastole** when the ventricles are relaxing; therefore, no contraction is happening. - All four heart valves are closed, and ventricular pressure is decreasing, allowing for ventricular filling to occur next. *Ventricular ejection phase* - In this phase, the **semilunar valves are open**, and blood is actively ejected from the ventricles into the aorta and pulmonary artery. - This occurs *after* isovolumetric contraction, once ventricular pressure exceeds arterial pressure. *Atrial contraction phase* - This phase involves the **atria contracting** to push the last bit of blood into the ventricles, representing the final stage of ventricular filling. - The ventricles are relaxed and filling during this time, not contracting.

Question 786: The Bainbridge reflex is triggered by:

A. Stretching of the atria (Correct Answer)
B. Baroreceptor reflex activation
C. Decreased venous return
D. Increased ventricular activity

Explanation: ***Stretching of the atria*** - The Bainbridge reflex, also known as the **atrial reflex**, is a neurogenic reflex initiated by an increase in intravascular volume, which leads to **distension of the right atrial wall**. - This stretching activates **stretch receptors** in the atria, primarily the right atrium, sending signals via the vagus nerve to the medulla oblongata, resulting in an **increase in heart rate**. *Baroreceptor reflex activation* - The **baroreceptor reflex** is primarily triggered by changes in **arterial blood pressure**, detected by stretch receptors in the carotid sinus and aortic arch. - Its main function is to stabilize blood pressure, often leading to a **decrease in heart rate** in response to high blood pressure, which is opposite to the Bainbridge reflex. *Decreased venous return* - **Decreased venous return** would lead to reduced filling of the atria and ventricles, which would **not stimulate atrial stretch receptors** to activate the Bainbridge reflex. - Instead, decreased venous return typically **reduces cardiac output** and can trigger other compensatory mechanisms like vasoconstriction and increased heart rate via different pathways. *Increased ventricular activity* - While increased ventricular activity is a result of an increased heart rate, it is **not the trigger** for the Bainbridge reflex itself. - The reflex is initiated by changes in **atrial volume and stretch**, not ventricular action.

Question 787: A 25-year-old athlete undergoing endurance training is most likely to experience which of the following cardiovascular adaptations?

A. Increased resting heart rate
B. Increased stroke volume (Correct Answer)
C. Decreased cardiac output
D. Decreased myocardial contractility

Explanation: ***Increased stroke volume*** - Endurance training leads to **cardiac hypertrophy**, particularly of the left ventricle, which increases its capacity to fill with blood. - A larger and stronger ventricle can eject more blood per beat, resulting in a **higher stroke volume** at rest and during exercise. *Increased resting heart rate* - Endurance training typically causes a **decrease in resting heart rate** (bradycardia) due to increased parasympathetic tone and improved cardiac efficiency. - A lower heart rate allows for more time for ventricular filling, further contributing to increased stroke volume. *Decreased cardiac output* - **Cardiac output** (heart rate × stroke volume) is maintained or even increased during exercise in trained individuals, especially at maximal effort. - At rest, while heart rate decreases, the significant increase in stroke volume usually ensures that resting cardiac output is similar or slightly higher than in untrained individuals, not decreased. *Decreased myocardial contractility* - Endurance training generally enhances **myocardial contractility** and efficiency, allowing the heart to pump blood more effectively. - A decrease in contractility would be detrimental to exercise performance and is not an adaptation to training.

Question 788: Which physiological response is most directly associated with the initial stage of shock?

A. Vasodilation
B. Bradycardia
C. Tachycardia (Correct Answer)
D. Hypotension

Explanation: ***Tachycardia*** - **Tachycardia** is the primary compensatory mechanism in the initial stage of shock, aimed at maintaining **cardiac output** when **stroke volume** is reduced. - The **baroreceptor reflex** detects decreased blood pressure and stimulates the **sympathetic nervous system**, leading to increased heart rate. *Vasodilation* - **Vasodilation** typically occurs in specific types of shock, such as **septic** or **anaphylactic shock**, and is not a universal initial response. - In most forms of initial shock (e.g., **hypovolemic**, **cardiogenic**), the body attempts to compensate with **vasoconstriction** to maintain blood pressure. *Bradycardia* - **Bradycardia** is a decrease in heart rate and is generally counterproductive in the initial stages of shock where the body needs to increase **cardiac output**. - While some specific conditions might present with bradycardia (e.g., **neurogenic shock**), it is not the most direct or common initial physiological response to general shock. *Hypotension* - **Hypotension** is a defining clinical sign of shock, but it is a **consequence** of inadequate tissue perfusion, not an initial physiological response. - The body's initial physiological responses (like **tachycardia**) are aimed at preventing or compensating for **hypotension**.

Question 789: What is the primary function of the ductus arteriosus in fetal circulation?

A. Connect the pulmonary artery to the aorta (Correct Answer)
B. Connect the right atrium to the left atrium
C. Connect the pulmonary artery to the pulmonary vein
D. Connect the umbilical vein to the inferior vena cava

Explanation: ***Connect the pulmonary artery to the aorta*** - The **ductus arteriosus** is a fetal shunting vessel that connects the **pulmonary artery** directly to the **aorta**, bypassing the non-functional fetal lungs. - This allows most of the blood from the right ventricle to bypass the pulmonary circulation and enter systemic circulation. - After birth, the ductus arteriosus closes and becomes the **ligamentum arteriosum**. *Connect the right atrium to the left atrium* - This describes the function of the **foramen ovale** in fetal circulation, which shunts blood from the right atrium to the left atrium. - The foramen ovale eventually closes after birth to become the **fossa ovalis**. *Connect the pulmonary artery to the pulmonary vein* - There is no direct connection between the pulmonary artery and pulmonary vein in normal cardiovascular anatomy. - The pulmonary artery carries deoxygenated blood to the lungs, and the pulmonary vein carries oxygenated blood from the lungs to the heart. *Connect the umbilical vein to the inferior vena cava* - This describes the role of the **ductus venosus** in fetal circulation, which shunts oxygenated blood from the umbilical vein directly to the inferior vena cava, bypassing the fetal liver. - The ductus venosus becomes the **ligamentum venosum** after birth.

Question 790: What is the primary effect of increasing preload on the heart?

A. Decreased stroke volume
B. Increased stroke volume (Correct Answer)
C. Decreased heart rate
D. Increased heart rate

Explanation: ***Increased stroke volume*** - According to the **Frank-Starling law** of the heart, an increase in **venous return** (preload) stretches the cardiac muscle fibers, leading to a more forceful contraction. - This enhanced contractility results in a greater volume of blood ejected per beat, hence an **increased stroke volume**. *Decreased stroke volume* - This would occur if there was a sudden decrease in preload, or if contractility was impaired despite adequate preload. - Reduced stroke volume is generally a sign of cardiac dysfunction or insufficient filling. *Decreased heart rate* - Heart rate is primarily regulated by the **autonomic nervous system** and hormonal factors, not directly by preload. - While extreme changes in preload could indirectly affect heart rate, it is not the primary direct effect. *Increased heart rate* - An increased heart rate often occurs in response to exercise or stress, driven by the **sympathetic nervous system**. - While increased preload and heart rate can both contribute to increased cardiac output, increased heart rate is not the direct primary effect of preload itself.

Practice by Chapter

Cardiac Electrophysiology

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Cardiac Cycle

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Cardiac Output and Its Regulation

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Hemodynamics and Blood Flow

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Arterial System Physiology

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Microcirculation and Lymphatics

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Venous Return and Central Venous Pressure

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Cardiovascular Reflexes

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Regional Circulations

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Cardiovascular Responses to Exercise and Stress

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